1. Field of the Invention
The invention is directed to an improved fuel injection system for an internal combustion engine.
2. Description of the Prior Art
A fuel injection system known from EP 0 987 431 A2 has a high-pressure fuel pump and a fuel injection valve connected to it for each cylinder of the internal combustion engine. The high-pressure fuel pump has a pump piston that delimits a pump working chamber and is driven into a stroke motion by the engine. The fuel injection valve has a pressure chamber connected to the pump working chamber and an injection valve element that controls at least one injection opening; the pressure prevailing in the pressure chamber can move the injection valve element in the opening direction counter to a closing force in order to open the at least one injection opening. A first electrically actuated control valve controls a connection of the pump working chamber to a relief chamber and a second electrically actuated control valve controls a connection of a control pressure chamber to a relief chamber. A control piston delimits the control pressure chamber and the action of the pressure prevailing in the control pressure chamber on the control piston causes it to act on the injection valve element in a closing direction; the control piston can move in concert with the injection valve element. The control pressure chamber has a connection to the pump working chamber. For an injection of fuel, the first control valve is closed and the second control valve is opened so that high pressure cannot build up in the control pressure chamber and the fuel injection valve can open. When the second control valve is open, though, fuel flows out of the pump working chamber via the control pressure chamber, thus reducing the fuel quantity available for injection out of the fuel quantity supplied by the pump piston and also reducing the pressure available for the injection. It follows from this that the efficiency of the fuel injection system is not optimal.